The present invention relates to impact switches, and more particularly, to an annular impact switch for use in guided projectiles.
Guided projectiles utilize active or passive sensor systems, such as radar, laser, semi-active laser, or infrared, to detect a target and furnish guidance signals to home the projectile to impact with the target. These sensor systems require that a centerline segment of the nose of the guided projectile be transparent to a particular electromagnetic radiation wave band transmitted by, or reflected from, the target. In addition, these sensor systems require an electromagnetic radiation receptor disposed along the centerline of the guided projectile behind the transparent window of the nose to intercept the radiation transmitted by, or reflected from, the target. These requirements of sensor systems for a guided projectile seeker impose certain design constraints, i.e., a certain volume along the centerline at the nose of the guided projectile must be allocated to the sensor system. A guided projectile seeker uses a gyroscope with a rotating rotor magnet as a stabilizing mechanism as part of the guidance system. An impact switch in close proximity to the gyroscope must be designed so that it will not affect the functioning of the gyroscope. The design of an impact switch must also take into account the inertial effects acting upon the switch when the guided projectile is fired; acceleration forces of approximately 8,000 G's act on the projectile momentarily during the firing sequence. Finally, to achieve maximum warhead performance for a guided projectile having a shaped explosive charge, the explosive train of the projectile must be initiated within a very short period of time after the nose of the projectile impacts the target. An impact switch, by initiating near instantaneous detonation of the shaped explosive charge of the projectile upon impact with the target, causes the high-energy jet generated by the shaped explosive charge to be focused on the surface of the target to ensure maximum target penetration, and consequently, maximum target damage.
Typical impact switches, such as those disclosed in U.S. Pat. Nos. 3,842,222 to K. Hogland, 3,453,406 to K. Pope, and 3,158,705 to R. Bliss, utilize the force resulting from impact with an external object to deform a first element into contact with a second element to electrically activate a response circuit. The major limitation of these devices is that they are designed to function so that the impact force must be transmitted nearly perpendicularly from the point of impact to deform the first element. Due to the design constraints of guided projectiles, these types of impact switches would have to be positioned a significant distance rearward from the nose of the projectile if the impact force is to be transmitted approximately perpendicularly to the first element. Positioning the impact switch at a greater distance from the point of impact would decrease the performance of the warhead by increasing the initiation time of the explosive train due to the greater distance and intervening elements that the impact force would be transmitted through before acting to deform the first element into contact with the second element. The effect of this would be that the high-energy jet of the shaped explosive charge of a seeker guided projectile would not be focused on the surface of the target, but rather at a point behind the surface of the target which would attenuate the penetration capability of the projectile. Disposing these types of switches on the inner periphery of the nose of the projectile would result in added expense due to the number of switches required and the necessity of redundant hookups to the firing circuit of the projectile. In addition, the transmittal of the impact force at the periphery of the projectile nose may be other than approximately perpendicular to the first element which may result in a higher frequency of impact switch malfunction due to failure to deform the first element into contact with the second element. U.S. Pat. No. 3,158,705 also discloses an inertial switch for closing the firing circuit of a projectile when the projectile impacts the target at a graze angle. In addition to being limited in the same manner as impact switches, another disadvantage of inertial switches is the possibility of inadvertent activation of the firing circuit due to the inertial effects on the circuit closing elements of the inertial switch as the projectile experiences the high acceleration forces generated as the projectile is fired.